1. Field of the Invention
The present invention relates to optical communication, and more particularly, to a high-power hybrid optical transceiver module and a passive optical network (PON) system including the high-power hybrid optical transceiver module and having an improved optical network terminator (ONT) accommodation capability.
2. Description of the Related Art
Fiber To The Home (FTTH) technology is being actively studied and developed all over the world to connect a home to a telephone office using an optical fiber transmission line so as to provide integrated services including voice calls, data services, and broadcasts. The use of FTTH technology will be dramatically increased in the next several years. Particularly, a PON system is the most common FTTH system.
The main consideration in developing FTTH technology is to provide a cost-effective and highly-productive method of transmitting an optical signal in a subscriber line network. Although an wavelength division multiplexing (WDM)-FTTH system (e.g., WDM-PON system) can provide independent and high-capacity communication services for subscribers, the number and interval of wavelength bands available for the WDM-PON system is limited. Therefore, a limited number of subscribers can use the WDM-PON system.
Such disadvantages of the WDM-PON system can be reduced by applying a time division multiplexing access TDMA scheme to the WDM-PON system, and thus the WDM-PON system adapting the TDMA scheme is used as a standard communication method for PON systems. In a TDMA-PON system, a plurality of subscribers shares the same optical wavelength (band) for data transmission. Costs required for constructing a subscriber line network using a PON system are determined by the number of optical network terminals (ONTs) that can be connected to a single optical line terminal (OLT).
Generally, the number of ONTs that can be connected to an OLT is determined by the optical power output of the OLT, optical power losses resulted from optical splitting at a time division multiplexing (TDM) optical splitter, and the power budget for other optical links. For example, when a PON system having sixteen subscriber nodes (sixteen ONTs) requires an optical power level of 0 dBm for normal optical communication, a PON system having two ONTs requires a relatively low optical power level of −6 dBM, and a PON system having one hundred twenty eight ONTs requires a high optical power level of +10 dBm for normal optical communication. That is, a high optical output power level is required to connect many ONTs (e.g., 128 or more ONTs) to one OLT due to optical power losses.
Since there is a limit to increasing the optical output power of an optical transceiver in a PON system, PON systems having an OLT coupled with 16 to 32 ONTs are currently the most common. That is, conventional optical transceiver modules for OLTs have a low optical output power level of about +2 dBm.
The optical output power of an optical transceiver module can be increased by directly increasing the optical output power of a light source such as a laser diode (LD) of the optical transceiver or amplifying the optical output power of the LD using a optical amplifier.
However, both the methods have limits since the optical output power of the LD cannot be increased beyond a certain level, and the additional optical amplifier increases the cost and size of the optical transceiver module.
FIG. 1 illustrates a conventional high-power optical transceiver module.
Referring to FIG. 1, the conventional high-power optical transceiver module includes an optical signal generator 10 generating an optical signal having a predetermined wavelength and an optical amplifier 20 amplifying the optical signal generated from the optical signal generator 10. The optical signal generator 10 includes an LD converting an electric signal into an optical signal and a monitor photo diode (MPD) monitoring the optical signal of the LD.
The optical signal generated from the optical signal generator 10 is transmitted to the optical amplifier 20 through an optical cable 30. The optical amplifier 20 amplifies the optical signal transmitted from the optical signal generator 10 using a semiconductor optical amplifier (SOA).
The high-power optical transceiver module further includes optical connectors 12, 22, and 24. The optical connector 12 connects the optical signal generator 10 and the optical cable 30, and the optical connector 22 connects the cable 30 and the optical amplifier 20. The optical connector 24 connects the optical amplifier 20 to an ONT.
Since the optical signal generator 10 and the optical amplifier 20 are individually packaged in the high-power optical transceiver module, the manufacturing costs and size of the optical transceiver module increase.
FIG. 2 illustrates a conventional high-power optical transceiver module having a planar lightwave circuit (PLC) structure.
Referring to FIG. 2, the high-power optical transceiver module includes an LD 50, an SOA 60, a photo diode (PD) 70, and an optical coupler such as a wavelength division multiplex (WDM) coupler 80 that are integrated on a PLC platform as one package.
Meanwhile, the high-power optical transceiver module further includes an MPD 40 and an optical connector 95. A thermoelectric cooler 90 surrounds the high-power optical transceiver module to stabilize the optical wavelength and power of the optical transceiver module. An optical waveguide 30 is used to connect the components of the optical transceiver module. The optical waveguide 30 includes a first optical waveguide portion 32 located at a transmitting side for transmitting a wavelength signal, a second optical waveguide portion 34 located at a receiving side for receiving a wavelength signal, and a third optical waveguide portion 36 to which the first and second optical waveguide portions 32 and 34 are connected. Both transmitting and receiving wavelength signals are delivered through the third optical waveguide portion 36.
Although the optical transceiver module having the PLC structure is small and cost-effective, it is difficult to precisely arrange the components of the optical transceiver module since the LD 50 and the SOA 60 are formed together on the PLC platform and thus the optical output angles of the LD 50 and SOA 60 are narrow.